We would like to thank Rabah Amir, Francis Bloch, Gabrielle Demange, Maria Garcia-Alonso, Sanjeev Goyal, Matthew Elliott, Maia King, Judith Payne, Zaki Wahhaj, Kathy Yuan, Marco van der Leij, and participants at seminars at Amsterdam, Bath, Cambridge, Glasgow, LSE, Malaga, NYU阿布达比,巴黎,萨拉曼卡以及几次讲习班和会议,以获取宝贵的评论。